The present invention relates to radiation measurement apparatus, and more particularly to small, light-weight portable radiation measurement apparatus. Even more particularly, the present invention relates to a reliable, inexpensive, pocket sized, battery-powered dosimeter that provides an accurate, quantitative, digitally-displayed measure of radiation levels to which the device is exposed, and that can be easily and unobtrusively carried by an individual, e.g., in a shirt pocket.
In many occupations and/or environments, there is a need to monitor radiation levels to which personnel or equipment is exposed. In such instances, it is most useful to know actual (quantitative) radiation dosage. For example, variations and trends in radiation dosage may need to be quickly identified so that appropriate action can be taken, e.g., by removing personnel from areas where radiation is approaching (but not yet at) levels that could be hazardous to one's health; or by taking appropriate corrective action (such as shutting down or adjusting radiation-producing equipment) so that radiation levels are well below safe limits.
Unfortunately, radiation measurement devices of the prior art that provide accurate radiation dosage readings are typically large, expensive, bulky devices that consume more power than is generally available in small, portable, battery-powered devices. Hence, in order to monitor radiation dosages experienced by an ambulatory object, such as a person employed in an area where radioactive devices and/or material are used, it has been necessary to employ passive threshold-detection dosage indicators, i.e., non-power-consuming devices that have an indicator, usually a film, that changes color when exposed to radiation levels above a fixed threshold. Such passive indicators are advantageously light weight and can be easily carried by an individual, e.g., in a pocket or clipped to clothing, but they do not provide a quantitative measure of the radiation dosage. Further, passive indicators must be visually monitored to determine if the fixed radiation threshold has been exceeded. What is needed, therefore, is a light weight dosage indicator that can be carried as easily as the passive dosage indicators of the prior art, but that also provides an accurate quantitative measure of radiation dosage, as well as an audible alarm whenever a preset threshold of radiation dosage has been exceeded.
In order to provide an accurate quantitative measure of radiation dosage, it is known in the art to use a microprocessor within the radiation measurement device. In order to simplify the design of such microprocessor-based radiation apparatus, it is known to use the microprocessor itself to count the pulses from the radiation detector. The problem with this approach is that a microprocessor can accurately count pulses at only a small fraction of its clock frequency. Thus, the microprocessor can either be operated at a low frequency (and hence low power) and accept poor counting performance, or the microprocessor can be operated at a high clock frequency, to provide better counting performance, at the cost of much higher current drain on the battery. Neither choice is acceptable for portable battery-powered radiation apparatus. Hence, it is evident that what is needed is a microprocessor-based radiation measurement device that can operate at low power, yet still be able to accept high count rates.
Further, when microprocessor-based radiation measurement apparatus is employed, some means must be used to load data into such apparatus and read data out of such apparatus. Typically, this is accomplished using a serial communications port implemented with multi-pin connectors (which eventually wear out and fail), or with Light Emitting Diodes (LED's) and Photodetectors (which require an unobstructed optical path and relatively large amounts of power to function). Thus, where a light-weight, low-power microprocessor-based radiation measurement apparatus is employed, some means must be used to reliably enter data into and extract data from the microprocessor at low power levels.